[winswitch] Reducing the colour depth (client side)

[Nick Burrett]

On 4 March 2013 09:00, Antoine Martin <antoine at nagafix.co.uk> wrote:
> Hi Nick,
>
> xpra is a compositing window manager, and AFAIK this requires 24bpp or
> higher. I've tried launching Xvfb/Xdummy with 8bpp and Composite gets
> turned off. The -pixdepths switch does not help here. FYI: xpra seems to
> crash rather than exit gracefully, but that's another problem.
>
> As for achieving bandwidth savings by reducing the colour depth, x264
> and vpx encodings use colour subsampling when the quality is lowered
> (switching from 4:4:4 to 4:2:2 and 4:2:0), this is in the chroma+luma
> space rather than plain RGB, but it does save about 50% on image size.
> Also note that newer encodings (x264, webp, etc) are vastly superior to
> the encodings found in VNC, so the bandwidth usage should already be
> much lower (even without colour subsampling).

Alright, that makes sense.   My gnome-terminal data transfer showed as
420Mbytes for around 6 hours of operation (using x264).  I'll have a
go at tuning the quality some more and extend the time between full
window refreshes.

I wonder if there's some efficiency to be gained by pre-processing the
image before compression (at the expense of quality) -- perhaps by
masking out the bottom 3 bits of R, G and B values so that the
compressors don't have to try to handle subtle colour variations.

>
> If you find that the quality/bandwidth/framerate/latency isn't good
> enough for you use case, let me know - it is quite possible that recent
> versions have focused a little bit too much on the LAN usage scenario..

It's not great at the moment -- it can take 2-3 seconds to switch a
tab in gnome-terminal, for example.  But I'd rather ensure that I've
exhausted my client option settings first.

Regards,

Nick

>
>
> On 03/03/2013 07:26 PM, Nick Burrett wrote:
>> Hi,
>>
>> Is it possible to reduce the colour depth client side when performing
>> xpra attach?
>>
>> I'm attempting to use xpra over a 3G modem link where the X server is
>> 140ms away.  For a while, I've been using a VNC setup in exactly this
>> way and found that reducing the colour from 24bits to 8bits had a
>> considerable impact on usability.
>>
>> Xvfb has a -pixdepths option, which appears to be a list of supported
>> colour depths.  I just would like to get the client to allow the
>> choice to be determined at connection time.
>>
>> Regards,
>>
>> Nick.
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>>
>
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